High stability of performance in recording process and reproducing process of information is required for consumer optical disc apparatuses and optical disc apparatuses used for archiving data in business facilities such as data centers.
A digital video disc (DVD) and a Blu-ray disc (BD) among media used for optical disc apparatuses have large storage capacities. Therefore, it is expected that applications of optical disc apparatuses which uses a DVD and a BD to perform optical information process will greatly expand in future. Therefore, highly reliable optical disc apparatuses are required.
Dust is one of factors which make performance of an optical disc apparatus unstable. Dust may be removed to some extent during fabrication of an optical head which is incorporated in an optical disc apparatus or during fabrication of the optical disc apparatus. However, it is difficult to completely remove dust.
Even if dust is removed during the manufacturing process, the dust may adhere to an objective lens which is incorporated in the optical head/optical disc apparatus while the optical head or the optical disc apparatus is in use.
A hard disc drive device has a completely sealed structure into which a drive mechanism and a disc are integrated. Therefore, little dust adheres to an objective lens of the hard disc drive device. On the other hand, a medium (optical disc) used for an optical disc apparatus has to be ejected from the optical disc apparatus. Therefore, the optical disc is not sealed and fixed inside the optical disc apparatus. Accordingly, the optical disc apparatus is more likely to be susceptible to dust than the hard disc device is.
The optical head incorporated in the optical disc apparatus is used for recording information onto an optical disc and/or reproducing information from an optical disc. The optical disc apparatus includes a turntable and a spindle motor in addition to the optical head. The optical disc is mounted on the turntable. The spindle motor drives the turntable to rotate the optical disc. While the optical disc rotates, the optical disc apparatus moves the optical head in the radial direction of the optical disc to perform information process such as recording information onto the optical disc and/or reproducing information from the optical disc.
The optical disc apparatus includes a light source and a photo-receiver. The light source emits a laser beam. The objective lens incorporated in the optical head condenses the laser beams onto the recording surface of the optical disc. Information is written to the optical disc by condensing the laser beams onto the recording surface. Or, condensing the laser beams onto the recording surface results in reflected light which is reflected by the recording surface. The reflected light reaches the photo-receiver through the objective lens. The photo-receiver outputs signals in response to the reflected light. The optical disc apparatus may use the output signals from the photo-receiver to reproduce the information recorded on the optical disc.
Dust adhering to the objective lens interrupts propagation of light. Therefore, information process such as recording information onto the optical disc or reproducing information from the optical disc is likely to be susceptible to the dust. If the optical disc apparatus attempts to read signals (information) recorded on the optical disc using the reflected light under an environment in which dust adheres to the objective lens, there may be frequent signal read errors. In this case, a user mounts a cleaning disc on the optical disc apparatus to make a brush of the cleaning disc contact the objective lens. Consequently, the dust adhering to the objective lens may be removed (c.f. Patent Document 1).
A cleaning solution may be applied to the brush of the cleaning disc (wet type). Alternatively, the brush may rub against the objective lens without cleaning solution (dry type). In both cases of the wet and dry types, dust and dirt from the exhaust gas and smoke in the air may be removed from the objective lens by the brush contacting the objective lens.
According to Patent Document 1, the brush is situated near the inner edge of the cleaning disc. Since the position of the brush corresponds to a position of a management information area which is accessed to identify the medium, the brush may contact the objective lens.
FIG. 30 is a schematic cross-sectional view of a conventional optical disc apparatus 900. The optical disc apparatus 900 is described with reference to FIG. 30.
The optical disc apparatus 900 includes an objective lens 910, a lens holder 920, a protector 930, a spindle motor 940, a turntable 950 and a drive holder 960. An optical disc OD is mounted on the turntable 950. The spindle motor 940 rotates the turntable 950 and the optical disc OD.
The objective lens 910 and the protector 930 are attached to the lens holder 920. The cylindrical protector 930 surrounds the objective lens 910. The upper edge of the protector 930 is closer to the lower surface of the optical disc OD than the upper surface of the objective lens 910, which faces the lower surface of the optical disc OD. Therefore, the protector 930 may prevent contact between the objective lens 910 and the optical disc OD.
The drive holder 960 uses a holding wire (not shown) to elastically suspend the lens holder 920. The drive holder 960 moves the lens holder 920 and the objective lens 910 in the radial direction of the optical disc OD.
FIG. 31 is a schematic cross-sectional view of the optical disc apparatus 900 which is subjected to a dry type cleaning process. The cleaning process for the optical disc apparatus 900 is described with reference to FIGS. 30 and 31.
A cleaning disc DCD is mounted on the turntable 950 shown in FIG. 31, instead of the optical disc OD. The cleaning disc is provided with a cleaning brush DCB. The cleaning brush DCB gently rubs against the objective lens 910. Meanwhile, a pressing force (indicated by the arrow in FIG. 31), which acts on the objective lens 910, displaces the objective lens 910 downward. Consequently, the cleaning brush DCB may not apply a sufficient force to the objective lens 910 to remove dust and dirt from the objective lens 910.
FIG. 32 is a schematic cross-sectional view of the optical disc apparatus 900 which is subjected to a wet type cleaning process. The cleaning process for the optical disc apparatus 900 is described with reference to FIGS. 31 and 32.
A cleaning disc WCD is mounted on the turntable 950 shown in FIG. 32, instead of the cleaning disc DCD used for the dry type cleaning process. The cleaning disc WCD is provided with a cleaning brush WCB. Unlike the cleaning brush DCB used for the dry type cleaning process, a cleaning solution is applied to the cleaning brush WCB. The cleaning brush WCB gently rubs against the objective lens 910, like the cleaning brush DCB used for the dry type cleaning process. Meanwhile, a pressing force (indicted by the arrow in FIG. 32), which acts on the objective lens 910, displaces the objective lens 910 downward. Consequently, the cleaning brush WCB may not apply a sufficient force to the objective lens 910 to remove dust and dirt from the objective lens 910.
During the aforementioned cleaning processes, the objective lens 910 is fixedly held in a direction orthogonal to the optical axis. However, the objective lens 910 is elastically held in a direction parallel with the optical axis. Therefore, as described above, the objective lens 910 is displaced downward by the pressing force from the cleaning brush DCB or WCB. If the objective lens 910 displaces downward, the rubbing force applied to the objective lens 910 is weakened. Accordingly, the dust and dirt may not be removed from the objective lens 910.
If an excessively strong force is applied to the objective lens 910, plastic deformation may happen to a support member configured to elastically support the objective lens 910. An objective lens of an optical disc apparatus which uses a BD has a very short working distance, in comparison with an optical disc apparatus which uses a DVD. For example, a working distance of an optical disc apparatus for a DVD is set to approximately 1.5 mm whereas a working distance of an optical disc apparatus for a BD is set to a value in a range from 0.2 mm to 0.3 mm. Therefore, if a cleaning disc DCD or WCD which has a cleaning brush DCB or WCB is used for cleaning an objective lens of an optical disc apparatus which uses a BD, an excessively strong pressing force is likely to be applied to the objective lens 910. The excessively strong pressing force may make a focus setting of the objective lens 910 inappropriate. The pressing force may damage an actuator for driving the lens.
FIG. 33 is a schematic cross-sectional view of the optical disc apparatus 900 which is subjected to the wet type cleaning process. Problems of the conventional cleaning process are described with reference to FIGS. 30 to 33. The problems described with reference to FIG. 33 are in common with the dry type cleaning process.
The cleaning brush WCB may apply a diagonal pressing force (indicated by the arrow in FIG. 33) to the objective lens 910. In this case, a torsional force is applied to the lens holder 920 which holds the objective lens 910. The torsional force may result in plastic deformation happening to the holding wire which suspends the lens holder 920.
The plastic deformation of the holding wire causes the objective lens 910 to execute an inappropriate focusing and/or tracking operations. In short, the objective lens 910 of the optical disc apparatus 900 after the cleaning process may not track the optical disc OD appropriately.
Contact of the cleaning brush DCB or WCB with the objective lens 910 may scratch a surface of the objective lens 910. Scratches may severely deteriorate reproduction performance of the optical disc apparatus. If the objective lens 910 is made of resin, scratches are likely to result from the contact of the objective lens 910 with the cleaning brush DCB or WCB.
An anti-reflection film is deposited on a surface of the objective lens 910 in consideration of transmittance, stray light and aberrations. The contact of the cleaning brush DCB or WCB with the objective lens 910 may result in dissipation of the anti-reflection film from the surface of the objective lens 910. Consequently, the optical transmittance of the objective lens 910 may drastically drop. Or, stray light may drastically increase because of scattered luminous flux resultant from the dissipation of the anti-reflection film. The dissipation of the anti-reflection film may cause a drastic growth in aberration. These changes in optical characteristics may drastically deteriorate the recording performance to record information onto the optical disc OD and the reproducing performance to reproduce information from the optical disc OD.    Patent Document 1: JP 2008-112498 A